As a mechanism to carry information over long distances, store-and-forward (S&F) networks offer an efficient, low-cost alternative to the existing public switched telephone network (PSTN). In general, S&F networks operate parallel to, and are accessed by, the PSTN.
FIG. 1 shows schematically PSTN 30 and S&F network 80 connected in parallel between a source fax machine 10 and a destination fax machine 70. An autodialer 12, positioned between the source fax machine and PSTN 30, designates incoming faxes for transmission over either the PSTN 30 or S&F network 80. If for example the destination of the incoming fax is not one serviced by the S&F network, then the autodialer dials the destination fax number directly to the local exchange 32; the call is then carried in a normal fashion by the PSTN 30 to the destination local exchange 36 and the destination fax machine 70. In contrast, if the number is one serviced by the S&F network, the autodialer dials the telephone number corresponding to that of the source network node 20. The local exchange 32 then routes the call through the PSTN to the source node. (Note that, depending upon their proximity, the source fax machine 10 and the source network node 20 may be served by the same or different local exchanges.) Once it has completely received the document, the source node 20 transfers it to the destination network node 40 over dedicated circuit 60. At this point, the destination node 40 dials the destination fax number to its local exchange which in turn transfers the call via the PSTN to the destination fax machine 70. (Note again that, depending upon their proximity, the destination fax machine 70 and the destination network node 40 may be served by the same or different local exchanges.)
In summary, transport of information from the source fax machine to the destination fax machine using the S&F network requires three distinct steps:
(1) transport from the source fax machine to the source network node via the PSTN; PA1 (2) transport from the source node to the destination node via dedicated circuits; and PA1 (3) transport from the destination node to the destination fax machine, again via the PSTN.
Store-and-forward networks offer a number of significant advantages over standard telephone networks for transport of facsimile. For example, a fax document can be carried 16 times more efficiently using technology employed by S&F networks. A common annoyance in telephony is the inability to complete a call, usually because the destination device is busy or does not answer. Although sophisticated voice mail systems have been designed to overcome this problem in voice telephony, similar practical and cost effective solutions do not exist for fax. S&F networks offer a viable solution. A properly implemented S&F network will employ a sufficiently large number of telephone circuits such that a customer fax machine never encounters a busy signal when attempting to send a fax via the network. At the destination end, it is a common practice to design into S&F networks the ability to automatically redial those call attempts which encounter "busy" or "no-answer" signals. Normally, the calls are redialed periodically over a fixed interval of time, every ten minutes for a half hour, for example.
Since multiple messages are typically coursing through an S&F network at any point in time, it is important to have some mechanism to monitor the location and status of each. For example, in one known S&F network, a small data file called an envelope is created to track each fax document as it moves through the network. The source node creates the envelope after it receives an incoming fax document. As the fax document moves through the network, the envelope moves between the network devices and receives continuous updates regarding the status of the fax. This enables substantially real-time monitoring of the fax delivery process.
In the known S&F network, upon concluding the delivery attempt process, the destination network node declares the fax document either "delivered" or "not delivered"; it records the status in the corresponding envelope which is then returned to the source node. If the delivery was successful, the envelope is forwarded to a historical database (HD) which provides a basis for constructing customer bills. If the delivery was not successful, the envelope is forwarded to a delivery assist system (DAS) for further processing. DAS is a database management system which provides a human operator, the document delivery analyst, with the delivery history and options for resubmission to the network of the document in question. One of the possible actions the analyst may take is to assign the fax document to an alternate destination number, i.e., one provided by either the sender or the receiver.
Wrong numbers, i.e., destination numbers that do not terminate on the fax machine, add enormously to the cost of delivery on a store-and-forward network. For example, it has been determined that up to 40% of delivery problems have been associated with mis-dialed fax numbers. Wrong numbers may be significantly reduced by requiring the customer to provide a list of commonly used fax numbers which is then entered into the autodialer memory or database. Upon receiving a dialed number from the attached fax machine, the autodialer compares it to its database; if a match is found, the call is transferred to the S&F network. However, this method places a considerable burden on the customer to provide a complete list of validated fax numbers, which may change over time. In addition, there is the problem of entering the numbers in each autodialer, which for a customer with a large number of fax machines, is expensive and time-consuming.
Another method of determining valid fax numbers is for the autodialer itself to qualify numbers. In this method, when the autodialer receives a fax number which is not part of its database, it routes the fax number to the PSTN, and monitors the call to determine if the destination is a fax machine; if so, it adds the number to its database. Thus, the next time this autodialer receives a call for that destination, the number is found in its database and the call consequently routed to the S&F network. There is no need to burden the customer with providing endless lists of valid numbers.
The above methodology has a deficiency, however. It is common for organizations to utilize more than one fax machine; indeed, in some cases the machines number in the hundreds. Often, fax documents are sent to the same destinations from many or all of the machines. Because each fax machine is served by its own autodialer, a destination telephone number could theoretically require requalification as many times as the number of fax machines in the organization. Clearly this is disadvantageous to both the customer and the network operator. The customer is deprived of the savings and higher quality service each time a call is unnecessarily requalified. The network operator is not only deprived of the additional revenue but, more importantly, appears inefficient as a service provider.